In intensive vegetable crops, there is a requirement for monitoring tools that assess crop nitrogen (N) status to reduce N use and the potential for nitrate (NO) leaching loss. Monitoring with proximal optical sensors can regularly provide information to vegetable growers to assist with optimal crop N management. Reference values for proximal optical sensor measurements that indicate crop N sufficiency or deficiency are increasingly available in the literature. Available values are species specific; however, their use may be problematic if proximal optical sensor measurements are affected by cultivar. Little is known on whether differences between cultivars, within a species, affect optical sensor measurements and their relationships with crop N status, particularly in vegetable crops. This study evaluated the effect of cultivar on a) measurements with the SPAD-502 chlorophyll meter, Normalized Difference Vegetation Index (NDVI) measured with the Crop Circle ACS 470 canopy reflectance sensor, and Nitrogen Balance Index (NBI-R) measured with the Multiplex fluorimeter, and b) the relationships of these measurements with leaf N content. The study was conducted with four cultivars of muskmelon (Tezac, Bosito, Magiar and Jacobo) and three of sweet pepper (Melchor, Machado and CLX PLRJ 731). In both muskmelon and sweet pepper, there were significant differences between cultivars in SPAD and in NBI-R. The range of differences between the cultivars was 2.2−9.7 and 0.6−2.8 SPAD units in muskmelon and sweet pepper, respectively, and 0−0.16 and 0.020.08 NBI-R units in muskmelon and sweet pepper, respectively. Significant differences between cultivars in the NDVI were only obtained in muskmelon; the range of differences between the four cultivars was 0.01–0.04 NDVI units. The relatively large cultivar effect with SPAD and NBI-R values with muskmelon may limit the use of reference values in this species. For avoiding cultivar effects in the two species evaluated, NDVI is preferrable to SPAD and NBI-R. In general, the slopes and intercepts of linear relationships between optical sensor measurements and leaf N content, for each cultivar of each species, were not significantly different to the slope and intercept of the relationship calculated with pooled data of all cultivars of each species. This indicated that the sensitivity of optical sensors to assess leaf N content was similar between cultivars of each species.

中文翻译：

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品种对甜瓜和甜椒近端光学传感器测量和叶片氮含量估算的影响


在集约化蔬菜作物中，需要评估作物氮 (N) 状况的监测工具，以减少氮的使用和硝酸盐 (NO) 淋溶损失的可能性。使用近端光学传感器进行监测可以定期向蔬菜种植者提供信息，以协助优化作物氮素管理。文献中越来越多地提供近端光学传感器测量的参考值，表明作物氮充足或缺乏。可用值因物种而异；然而，如果近端光学传感器测量受到品种的影响，它们的使用可能会出现问题。关于一个物种内品种之间的差异是否会影响光学传感器测量及其与作物氮状态的关系，尤其是蔬菜作物，人们知之甚少。本研究评估了品种对 a) 使用 SPAD-502 叶绿素计测量、使用 Crop Circle ACS 470 冠层反射传感器测量的归一化植被指数 (NDVI) 以及使用 Multiplex 测量的氮平衡指数 (NBI-R) 的影响荧光计，b) 这些测量值与叶片氮含量的关系。该研究针对四个甜瓜品种（Tezac、Bosito、Magiar 和 Jacobo）和三个甜椒品种（Melchor、Machado 和 CLX PLRJ 731）进行。在甜瓜和甜椒中，SPAD 和 NBI-R 品种之间存在显着差异。甜瓜和甜椒品种之间的差异范围分别为 2.2−9.7 和 0.6−2.8 SPAD 单位，甜瓜和甜椒分别为 0−0.16 和 0.020.08 NBI-R 单位。仅在甜瓜中获得了品种间 NDVI 的显着差异；四个品种之间的差异范围为 0.01-0.04 NDVI 单位。 甜瓜的 SPAD 和 NBI-R 值相对较大的品种效应可能会限制参考值在该物种中的使用。为了避免对所评估的两个物种产生品种影响，NDVI 优于 SPAD 和 NBI-R。一般来说，对于每个物种的每个品种，光学传感器测量值与叶片氮含量之间的线性关系的斜率和截距与利用每个物种的所有品种的汇总数据计算的关系的斜率和截距没有显着差异。这表明光学传感器评估叶片氮含量的灵敏度在每个物种的品种之间是相似的。